In the past, reversible plows have been developed which will selectively direct the plowed ground in one direction or the other. For example, U.S. Pat. No. 4,800,963 issued Jan. 31, 1989 to Pompeyo B. Gomez discloses a reversible plow in which a tool bar carries a plurality of moldboards which are mounted in alignment with each other at evenly spaced locations along the length of the tool bar, with two moldboards being forward of a central pivot pin and two moldboards being rearward of the central pivot pin. A main frame carries the moldboard frame while a reversing arm, which cooperates with the moldboard frame and is operated hydraulically, pivots the moldboard frame from one angular position to the other with respect to the frame.
Such reversible plows typically have the moldboards pivotally mounted to support shanks which in turn depend from and are rigidly secured to the tool bar. The moldboards are secured against rotation by a shear pin or shear bolt fastening the moldboard to its respective support shank. With this construction, in the event the moldboard strikes a heavy object while plowing, the resulting forces act to shear off the shear pin and large-scale damage to the plow should be avoided. Unfortunately, replacing sheared off shear bolts in the field can be troublesome and too often some damage is done to the moldboard or to its support shank.
U.S. Pat. No. 3,910,354 of Johnson et al. discloses a toggle trip for a moldboard plow in which a normally over-center toggle mechanism can be tripped by forces resulting from the moldboard striking an unyielding object in the soil. In such an instance, a heavy leaf spring is straightened out, thereby pulling the toggle mechanism from its over-center position toward an under-center position to allow the toggle mechanism and the moldboard to be swung up and out of the way of the unyielding object. The structure disclosed in the patent is generally complex, much of which structure is positioned above the tool bar, thereby posing a potential clearance problem with other equipment to be mounted to the tool bar, such as a gauge wheel mounting arm.